This invention relates to a device to detect and analyze mechanical vibrations, and more particularly to a vibration analyzing device in which a vibration pickup part and an associated electric circuit are integrated in and upon a semiconductor substrate.
To detect mechanical vibrations for the purpose of extracting a specific frequency component or analyzing the vibration spectrum, it is customary to use a combination of a transducer which converts mechanical vibration into electrical signal and at least one band-pass filter for frequency discrimination of the signal produced by the transducer. Piezo-electric and some other types of transducers are available for this purpose, and in general such transducers are so devised as to possess a flat response characteristic over a relatively wide range of frequency.
In measuring mechanical vibrations by using a conventional instrument the transducer is attached to the object of measurement. Where the object of measurement is small in size and light in weight and particularly when it is intended to detect even minute vibrations of the small-sized object, the transducer is required to be very small in both size and mass. If this requirement is not met the attachment of the transducer results in a change in the vibration characteristics of the object of measurement, and therefore it becomes impossible to achieve accurate measurement of the vibrations. This manner applies also in the treatment of the lead wires extended from the transducer, so that the lead wires must be treated so as not to affect the vibrations of the object of measurement. Therefore, the conventional transducers are not always suitable for specific applications, for example for installation in a motor vehicle to analyze vibrations attributed to the operation of the engine.
In a vibration analyzer in which the electrical output of the transducer is transmitted to a band-pass filter or a plurality of band-pass filters via lead wires, the lead wires need to be made practically insusceptible to external noises since the output signal of the transducer is susceptible to noises especially when the signal is very weak. Therefore, the lead wires including some shield are liable to become considerably thick, and then undesirable influences of the lead wires on the vibration characteristics of the object of measurement will become serious in some cases. Where it is intended to perform minute analysis of the vibration spectrum, it is necessary to use a number of band-pass filters each of which is produced with very high precision. Naturally the circuit construction of the entire band-pass filters becomes very complicated with the need of using a large number of circuit elements. Then, besides an inevitable rise in the cost, the electric circuit including the band-pass filters occupies a considerable space and has considerable restrictions as to the placement thereof. Of course it is impracticable to mount the transducer and all the band-pass filters on a single circuit board which is suitable for attachment to the object of vibration measurement.